2-Bulb Temperature: Operation

When the ignition switch is turned to the start position, a test circuit is closed to determine if red light is functioning properly. When a cold engine is started, the bi-metal strip closes the circuit to the green (or blue) light, causing the green (or blue) light to burn indicating that the engine is not up to operating temperature and this light remains on until the engine reaches operating temperature. If the engine reaches an abnormally high temperature, the bi-metal strip closes the circuit to the red light, causing the red light to burn indicating that the engine temperature is abnormally high.